In a conventional damping device of this kind, as schematically and exemplarily shown in FIG. 1, guide rails 2 are mounted on a top surface of a structure 1 in parallel with a direction of oscillation of the structure 1, and a damping body or weight 3 rests against the rails 2 via wheels 4 horizontally movably along the rails 2. Interposed between an end face of the damping body 3 and a support frame 5 erected on the structure 1 on its one side in the direction of motion of the damping body 3 are an attenuator or damper 6 for attenuation of kinetic energy of the damping body 3 and a spring 7 for adjusting a characteristic frequency of the damping body 3. When oscillation of the structure 1 occurs, its oscillation energy is transmitted to the damping body 3 so that the damping body 3 is reciprocated on the guide rails 2 with delayed phase of 90° to the oscillation of the structure 1. Then, the kinetic energy of the damping body 3 is attenuated by the attenuator 6 to suppress the oscillation of the structure 1.
However, such damping device has a problem that mass, movement stroke and/or the like of the damping body 3 must be selected to afford an optimum damping effect to the structure 1 and a characteristic frequency of the damping body 3 must be matched with that of the structure 1, which adjustments are much difficult to perform.
More specifically, in the above-mentioned damping device, the characteristic frequency ω0 of the damping body 3 is given by the equationω0=(k/m)1/2 
and attenuation coefficient μ is given by the equationM=c/{2(mk)1/2}
where m is mass of the damping body 3, k is spring constant of the characteristic-frequency adjusting spring 7 and c is an attenuating or controlling force of the attenuator 6 for attenuating the oscillation of the damping body 3. When the characteristic frequency ω0 of the damping body 3 is to be changed, the spring constant of the spring 7 may be changed from k to k1 to attain change of the characteristic frequency into ω0′=(k1/m)1/2. Such change of k into k1 may be performed by changing the force of the spring 7, which in turn may require adjustment of spring displacement. However, the change of the spring constant from k into k.sub.1 is accompanied with change of expansion/contraction stroke of the spring 7, which in turn constrains the motion of the damping body 3, leading to the lowered damping effect. Thus, in particular, the structure 1 with a lower characteristic frequency tends to have mechanical restrictions on the spring 7. For example, when the expansion/contraction stroke of the spring 7 is to be set to 100 mm, generally the spring 7 is required to have length five times as much into 500 mm, leading to a problem of increased two-dimensional space required for installation of the device as a whole.
As a damping device capable of setting a characteristic frequency of a damping body with no mechanical restrictions on spring, there has been proposed, for example, a damping device as schematically shown in FIG. 2 in which a damping body 8 with an arched bottom having radius of curvature R rests against two support rollers 9 arranged in a mutually spaced-apart relationship on a structure 1 so as to allow free oscillation into simple harmonic oscillation, or a damping device as schematically shown in FIG. 3 in which a damping body 10 with a V-shaped bottom of angle θ as damping mass equivalently analogous to simple pendulum rests against two support rollers 9 on a structure 1 so as to allow free oscillation.
However, these simple-harmonic oscillation type damping devices have a problem that characteristic frequency is hard to adjust after the radius of curvature R of the damping body 8 or the angle θ of the damping body 10 is once decided.
Moreover, as mentioned above, when the characteristic frequency ω0 of the damping body 3 is to be changed, such change may be obtained into ω0′=(k1/m)1/2 by changing the spring constant of the spring 7 from k to k1. In this respect, since the actual characteristic frequency of the structure 1 is not necessarily as designed, a plurality of springs 7 with different spring constants are needed to be prepared so as to choose one of the springs 7 which has the characteristic frequency corresponding to that of the structure 1; and whenever the characteristic frequency of the damping body 3 is required to be adjusted in response to change in characteristic frequency of the structure 1, the spring 7 must be replaced by that with a corresponding spring constant.
As a damping device capable of both setting and adjusting the characteristic frequency of a damping body irrespective of a spring constant of a spring, there has been proposed a damping device as schematically shown in FIG. 4 in which a damping body 10 with a V-shaped bottom as equivalently analogous to simple pendulum rests via liner plates 10a against two support rollers 9 which in turn are arranged in a mutually spaced-apart relationship on a structure 1 so as to allow free oscillation. In this damping device, adjustment of the characteristic frequency of the damping body 10 requires replacement of the liner plates 10a with those having different thickness, which replacement work is extremely troublesome in that large scale equipment and tools such as hydraulic jacks, lever blocks and/or chain blocks are needed at a site.
Thus, a primary object of the invention is to provide a damping device comprising a damping body adapted for horizontal reciprocal movement and a spring or springs for adjusting a characteristic frequency of the damping body and which allows the motion of the damping body not to be restricted even when spring constant and/or expansion/contraction stroke of the spring or springs is changed.
A second object of the invention is, in a damping device comprising a damping body adapted for horizontal reciprocal movement and a spring or springs for adjusting a characteristic frequency of the damping body, to provide a method for setting the characteristic frequency of the damping body in which the characteristic frequency of the damping body can be readily set and adjusted.